Breast cancer is a heterogeneous group of tumors which can be subdivided on the basis of histopathological features, genetic alterations, and gene-expression profiles (1; 2). Approximately 50-60% of all breast cancer patients and two-thirds of postmenopausal breast cancer patients have estrogen receptor positive tumors (ER+). Adjuvant hormonal therapy is the primary therapy for ER+ breast cancer. TNBC is defined by the absence of staining for estrogen receptors, progesterone receptors, and HER2/neu. These tumors have poor clinical outcome and represent a recognized prognostic group characterized by aggressiveness (3) and resistance to available systemic therapy. Approximately 10-25% of all breast cancers in the U.S. are TNBC.
Current therapies for certain subtypes of breast cancer (BC), such as triple negative BC (TNBC) and other aggressive phenotypes, rely on standard chemotherapy approaches with significant side effects; therefore, newer targeted therapy approaches are needed.